A packet-based communications network makes provision to transmit packets between various nodes in a communications network. A packet comprises a group of bits, the group being of any fixed or variable size. Among examples of packet-based networks, there exist in particular: frame relay networks, in which a packet corresponds to a frame relay frame; cell-switching networks, e.g. asynchronous transfer mode (ATM) networks, in which a packet corresponds to an ATM cell; etc. A node may be defined as being a termination point for two or more channels or lines, and it generally includes control equipment.
Within a packet-based communications network, a virtual connection (VC) is set up between a source node and a destination node, and it generally passes through one or more intermediate nodes. A virtual connection is a logic connection (channel) between the source node and the destination node, enabling packets to be transmitted therebetween. Each node in the virtual connection acts as a packet interchanger for receiving a packet and sending it to its destination node. Each node in the communications network may be part of a diversity of virtual connections. The terminal nodes, such as the source node and the destination node, have interface cards that are necessary for receiving pre-formatted packets, and/or for correctly formatting the data contained in a conventional user data stream, so as to obtain packets, and/or to reassemble packets so as to obtain the conventional user data streams.
Packet-based communications networks are capable of combining a diversity of data such as local area network data, voice data, and image/video data into packets for the purpose of transmitting it over high-speed digital junctions. Each source node and each destination node is connected to various types of customer-premises equipment (CPE) such as a local area network, facsimile/modem equipment, voice equipment and image/video equipment, and other types of packet and/or data equipment for the purpose of transmitting corresponding packets via the communications network to a destination node.
In such packet-based networks, it is important to provide protocols suitable for managing traffic and for controlling congestion of packets travelling via a virtual connection. Various methods have been developed for controlling the rates at which packets are transmitted over a virtual connection, and also for controlling selective elimination of packets for the purposes of managing and controlling packet congestion.
One approach to managing and controlling packet congestion consists in a credit-based approach. The credit-based approach is a protocol which acts between adjacent nodes identified respectively as a “transmitter” and as a “receiver”, in which protocol a packet is transmitted between a transmitter and a receiver only if the transmitter knows that the receiver can accept the information without losses. The receiver sends control information to the transmitter by indicating whether it is capable of accepting new packets. The credit-based approach does not rely on end-to-end signalling to cope with congestion. In such a credit-based approach, closed-loop control of the transmitter is implemented so that the data is sent as quickly as possible without data loss, from the transmitter to the receiver.
Another approach to managing congestion is an information feedback approach in which the state of congestion of the virtual connection is measured as the packets are flowing in a go direction, from the source node to the destination node, and the state of congestion as measured is sent back from the destination node to the source node so as to adjust the rate at which packets are sent over the network.
This approach is described in the Applicant's European Patent Application No. 0 719 012. Unfortunately, the teaching of that Application is not relevant to the problem with which the present invention is concerned.